Dellagiustaite: A Novel Natural Spinel Containing V2+

Abstract

Dellagiustaite, ideally Al2V2+O4, is a new spinel-group mineral from Sierra de Comechingones, San Luis, Argentina, where it is found associated with hibonite (containing tubular inclusions, 5–100 μm, of metallic vanadium), grossite, and two other unknown phases with ideal stoichiometry of Ca2Al3O6F and Ca2Al2SiO7. A very similar rock containing dellagiustaite has been found at Mt Carmel (northern Israel), where super-reduced mineral assemblages have crystallized from high-T melts trapped in corundum aggregates (micro-xenoliths) within picritic-tholeiitic lavas ejected from Cretaceous volcanoes. In the holotype, euhedral grains of dellagiustaite are found as inclusions in grossite. The empirical average chemical formula of dellagiustaite is (Al1.09 V 0.91 2 + V 0.87 3 + Mg0.08 Ti 0.04 3 + Mn0.01)Σ3O4, but it may show limited replacement of V2+ by Mg and of V3+ by Al. As Al is the dominant trivalent cation, the ideal formula is Al2V2+O4 according to the current IMA rules. Dellagiustaite shows the usual space group of spinel-group minerals (Fd 3 ¯ m, R1 = 1.46%) with a = 8.1950(1) Å. The observed mean bond lengths <T–O> = 1.782(2) Å and <M–O> = 2.0445(9) Å, the observed site scattering (T = 13.3 eps, M = 22.5 eps), and the chemical composition show that dellagiustaite is an inverse spinel: T tetrahedra are occupied by Al3+, whereas M octahedra are occupied by V2+ and V3+, leading to the site assignment as TAlM( V 0.91 2 + V 0.88 3 + Al 0.09 3 + Mg0.08 Ti 0.03 3 + Mn0.01)O4.

Vanadium-induced coloration in grossite (CaAl4O7) and hibonite (CaAl12O19)

“…The presence of V 2+ in hibonite could open an interesting subject of study for this mineral as an indicator of reducing conditions (i.e., low Eh) during the growth of particular mineralogical assemblages. It is worth to note that in samples from Sierra de Comechingones grossite crystallizes after hibonite and the V is only in V 3+ oxidation state, whereas it assumes both divalent and trivalent valence state in hibonite (as well as in dellagiustaite; Cámara et al 2019). In addition, reduction of V is also favored by low pH conditions (Huang et al 2015), which may provide essential information in hydrothermal systems.…”

“…Grossite constitutes the rock matrix and is purplish pink, strongly pleochroic, and it shows frequent inclusions of dellagiustaite and an Al-rich perovskite ( Fig. 4) (Cámara et al 2019). A suitable large crystal that is free of inclusions was chosen under a microscope for later analyses.…”

“…So far, it has been reported only in six localities: granulites from the type locality in Esiva eluvials in Madagascar (Delbos 1955), Furua granulites at the Ligama Hill, Morogoro Region, Tanzania (Masskant et al 1980), Mg-Al skarn iron deposits of the Fushan Mine, She County, Hebei, Handan, China (Cao et al 1997), Chyulu Hills volcanic field, Kenya (Ulianov et al 2005), Mandalay region of Myanmar (Nagashima et al 2010;Wild and Milisenda 2013), and Tashelginskoye Fe-(Co) deposits, Kemerovo Oblast, Gornaya Shoriya Region Russia (Konovalenko et al 2012). Very recently, the occurrence of hibonite and grossite samples from an exotic mineralization from Sierra de Comechingones, San Luis, Argentina has been reported; in addition to dellagiustaite (a new mineral of the spinel supergroup, ideally Al2V 2+ O4), hibonite and grossite are main phases (Cámara et al 2019). Comparable rocks have been reported to occur at Mt.…”

“…our sample, namely M2 (Al0.83Ti 4+ 0.17) vs. M2 (Al0.95V0.05) for Nagashima et al's and our hibonite samples, respectively. It seems improbable that V 3+ enters into a site with fourfold coordination because this cation usually avoids this type of coordination, e.g., see coulsonitic spinels or the recently found dellagiustaite where V 3+ and V 2+ occupy octahedral sites(Cámara et al 2019), and therefore this possibility needs to be further explored by optical spectroscopy.…”

Eliopoulosite, V7S8, A New Sulfide from the Podiform Chromitite of the Othrys Ophiolite, Greece

“…According to literature data [1][2][3][4][5][6][7][8] eliopoulosite is the ninth mineral containing V and S that has been accepted by IMA. Noteworthy, eliopoulosite is the second V 2+ -bearing mineral, the first being dellagiustaite, Al 2 VO 4 [35]. The presence of divalent V requires extremely reducing conditions (well below the iron-wüstite buffer).…”